3126B and 3126E On-highway Engines Caterpillar

Use this procedure under the following situation:

Use this procedure to determine if the following circuits are operating correctly:

• Torque limit switch

• Ignore brake/clutch switch

• Two-speed axle switch

• Diagnostic enable switch

• PTO Engine RPM Set Speed Input A Switch

• PTO Engine RPM Set Speed Input B Switch

The following background information is related to this procedure:

The ECM can use various inputs in a number of ways. The inputs depend on the parameter programming. Certain features are available on several different inputs. The configuration for the switch must match the actual switch installation in order for the switch to function properly.

Input 4 (Torque Limit Switch)

MAR98 and Newer Software

The torque limit switch provides a way to temporarily protect equipment from damage that is caused by applying too much torque. Torque limiting is typically used during PTO operation. Torque limiting can also be used when the PTO on/off switch is in the OFF position.

In order to use torque limiting, the parameter "Torque Limit" must be programmed. The "Torque Limit" parameter is located under the "Dedicated PTO Parameters". The default setting is 2712 N·m (2000 lb ft). The "Input # 4" parameter must be programmed to "Torque Limit Switch". If the "Input # 4" parameter is programmed to "None" (default), this feature is not used.

OCT01 Software

The parameter "Input # 4" has been replaced by the parameter "Torque Limit Switch". This parameter can be programmed to "J1/P1:7", "J1/P1:23", or "None".

Input 5 (Ignore Brake/Clutch Switch)

MAR98 and Newer Software

The ignore brake/clutch switch is typically used when the parameter "PTO Configuration" is programmed to "Cab Switches". This configuration requires mobile use of the vehicle during PTO operation. When the ignore brake/clutch switch is on, depressing the brake or the clutch will not disengage PTO operation or a set engine speed. If the "Input # 5" parameter is programmed to "None" (default), this feature is not used. For information on troubleshooting this switch, refer to Troubleshooting, "Ignore Brake/Clutch Switch Circuit - Test".

OCT01 Software

The parameter "Input # 5" has been replaced by the parameter "Ignore Brake/Clutch Switch". This parameter can be programmed to "J1/P1:47" or "None".

Input 6 (Two-Speed Axle Switch)

MAR98 and Newer Software

When a two-speed axle is used, the change in gear ratios from the main drive axle ratio will alter the calibration of the vehicle speed signal. When the two-speed axle switch is in the ON position, the ECM will automatically adjust the vehicle speed calibration. This will ensure that the ECM driven speedometer and the stored information in the ECM correctly reflect the actual vehicle speed. In order for this feature to function properly, the "Low Speed Range Axle Ratio" and "High Speed Range Axle Ratio" parameters must be programmed. If the "Input # 6" parameter is programmed to "None" (default), this feature is not used.

OCT01 Software

The parameter "Input # 6" has been replaced by the parameter "Two-Speed Axle Switch". This parameter can be programmed to "J1/P1:6" or "None".

Input 7 (Diagnostic Enable Switch)

JUL99 and Newer Software

The diagnostic enable switch is used to prompt diagnostic flash codes on the check engine lamp. For more information, refer toTroubleshooting, "Flash Programming" and Troubleshooting, "Check Engine Lamp or Warning Lamp is Malfunctioning". If the "Input # 7" parameter is programmed to "None" (default), then the feature is not used. If the "Input # 7" parameter is programmed to "Diagnostic Enable Switch", then the feature is available and the switch circuit should be connected to terminal 46 of the J1/P1 ECM vehicle harness connector.

OCT01 Software

The parameter "Input # 7" is no longer used. "Diagnostic Enable" is the parameter that is used to configure a diagnostic enable switch. This parameter can be programmed to "J1/P1:46", "J1939 Cab Controller", "J1939 Body Controller", "J1939 Instrument Cluster", or "None". For troubleshooting the J1939 options, refer to Troubleshooting, "Powertrain Data Link Circuit - Test".

JUL99 and Newer Software

"Input # 7" can be programmed to "Diagnostic Enable Switch" or to "PTO Engine RPM Set Speed Input A". If the "Input # 7" parameter is programmed to "PTO Engine RPM Set Speed Input A" the switch is used to control engine speed during PTO operation. The switch circuit should be connected to terminal 46 of the J1/P1 ECM vehicle harness connector. The "PTO Configuration" parameter must be programmed to "Cab Switches", "Remote Switches" or "Remote Throttle" and the "PTO Engine RPM Speed Input A" parameter must be programmed to a valid speed.

The "PTO Engine RPM Set Speed A" parameter requires an engine rpm to be programmed. The "PTO Engine RPM Set Speed A" parameter is located in the "Dedicated PTO Parameter Group". The "Input # 7" parameter is located in the "Input Selections Parameter Group". The engine will ramp up to the engine rpm that is programmed under the following conditions:

• The switch for the PTO Engine RPM Set Speed Input A Switch is in the ON position and the PTO on/off switch is then turned on.

• The switch for the PTO Engine RPM Set Speed Input A Switch is turned to the ON position when the PTO on/off switch is on.

The PTO on/off switch or the switch for the PTO Engine RPM Set Speed Input A must be cycled from the OFF position to the ON position in order to return to the programmed engine rpm if the PTO operation is disabled.

OCT01 Software

The parameter "Input # 7" is no longer used. "PTO Engine RPM Set Speed Input A" is the parameter that is used to configure a PTO Engine RPM Set Speed Input A switch. This parameter can be programmed to "J1/P1:46", or "None". The "PTO Configuration" parameter must be programmed to "Cab Switches", "Remote Switches" or "Remote Throttle" and the "PTO Engine RPM Speed A" parameter must be programmed to a valid speed.

Input 19 (PTO Engine RPM Set Speed Input B Switch)

JUL99 and Newer Personality Modules.

"Input # 19" can be programmed to "PTO Engine RPM Set Speed Input B" or to "None". If the "Input # 19" parameter is programmed to "PTO Engine RPM Set Speed Input B", the switch is used to control engine speed during PTO operation. The "PTO Configuration" parameter must be programmed to "Cab Switches", "Remote Switches" or "Remote Throttle" and the "PTO Engine RPM Speed B" parameter must be programmed to a valid speed.

The "PTO Engine RPM Set Speed B" parameter requires an engine rpm to be programmed. The "PTO Engine RPM Set Speed B" parameter is located in the "Dedicated PTO Parameter Group". The "PTO Engine RPM Set Speed Input B" parameter is located in the "Input Selections Parameter Group". The function of the switch for the "PTO Engine RPM Set Speed Input B" is similar to the function of the switch for the "PTO Engine RPM Set Speed Input A". The engine will operate at Set Speed "A" when both of the switches are on. If the "PTO Engine RPM Set Speed Input B" parameter is programmed to "None" (default), this feature is not used.

OCT01 Software

The parameter "Input # 19" is no longer used. "PTO Engine RPM Set Speed Input B" is the parameter that is used to configure a PTO Engine RPM Set Speed Input B switch. This parameter can be programmed to "J1/P1:7", "J1/P1:23", or "None". The "PTO Configuration" parameter must be programmed to "Cab Switches", "Remote Switches" or "Remote Throttle" and the "PTO Engine RPM Speed B" parameter must be programmed to a valid speed.

Note: The wiring for your particular application may be slightly different. The circuits for the sensor common are used interchangeably by the OEM of the vehicle. The following circuits are common within the ECM:

• The "Input Sensor Common 1" is terminal 18.

• The "Input Sensor Common 2" is terminal 3.

• The "AP Sensor/Switch Sensor Common" is terminal 5.

Illustration 1	g00728802
Schematic for Torque Limit Switch OCT01 Software may also be configured to use J1/P1:23 for the Torque Limit Switch.

Illustration 2	g00682286
Schematic for ignore brake/clutch switch

Illustration 3	g00682705
Schematic for Two Speed Axle Switch Circuit

Illustration 4	g00728804
Schematic for Diagnostic Enable Switch or the PTO Engine RPM Set Speed Input A Switch

Illustration 5	g00728803
Schematic for the PTO Engine RPM Set Speed Input B Switch OCT01 Software may also be configured to use J1/P1:7 for the PTO Engine RPM Set Speed Input B Switch.

Illustration 6	g00728814
Terminal Locations for ECM

Test Step 1. Inspect Electrical Connectors and Wiring

1. Thoroughly inspect the ECM vehicle harness connector J1/P1, the connectors, and the firewall bulkhead connectors. Refer to Troubleshooting, "Electrical Connectors - Inspect" for details.

2. Perform a 45 N (10 lb) pull test on each of the wires in the ECM connector that are associated with the suspect switch circuit.

3. Check the ECM connector (allen head screw) for the proper torque of 6.0 N·m (55 lb in).

4. Check the harness and the wiring for abrasion and for pinch points from the battery to the ECM. Then, check from the ignition key switch to the ECM.

   Refer to Illustration 6 for terminal locations for the ECM.

Expected Result:

All connectors, pins, and sockets are completely coupled and/or inserted, and the harness and wiring should be free of corrosion, abrasion or pinch points.

Results:

• OK - Proceed to Test Step 2.

• Not OK - Repair the wiring and connectors or replace the wiring or the connectors. Ensure that all of the seals are properly connected. Verify that the repair eliminates the problem.STOP

Test Step 2. Check the Switch Status on an Electronic Service Tool

1. Connect the electronic service tool to the cab data link connector.

2. Turn the ignition key switch to the ON position.

3. Operate the switch in the ON position and the OFF position.

4. View the switch status on the electronic service tool.

5. If the switch status indicates "Not Installed", then the switch parameter has not been programmed.

Expected Result:

The status screen should indicate "ON" if the switch is turned ON. The status screen should indicate "OFF" if the switch is OFF.

Results:

• Yes - The switch is operating normally. Continue troubleshooting if the original condition is not resolved.STOP

• No - The ECM is not reading the switch status change. Proceed to Test Step 3.

Test Step 3. Check the Switch Circuit for the ECM.

Illustration 7	g00682375
Connector for Breakout T

1. Turn the ignition key switch to the OFF position.

2. Install a breakout T to the ECM vehicle harness connector J1/P1.

3. Fabricate a jumper wire 100 mm (4 inch) long. Crimp a Deutsch pin to both ends of the wire.

4. Insert the jumper wire into the suspected terminal of the breakout T. Connect the other end of the jumper wire to terminal 5 in the breakout T. Terminal 5 is AP sensor/switch common.

5. Connect the electronic service tool to the cab data link connector.

6. Turn the ignition key switch to the ON position.

7. Alternately remove the jumper wire and then insert the jumper wire from terminal 5. At the same time, monitor the status screen on the electronic service tool.

Expected Result:

The switch status changes to "ON" with the jumper wire in place. The switch status changes to "OFF" when the jumper wire is removed.

Results:

• Yes - The ECM is functioning properly at this time. Proceed to Test Step 4.

• No - The ECM is not functioning properly.

  Repair: Perform the following repair:

  1. Temporarily connect a test ECM.

  2. Remove all jumpers and replace all connectors.

  3. Recheck the system for active diagnostic codes.

  4. Repeat the test step.

  5. If the problem is resolved with the test ECM, reconnect the suspect ECM.

  6. If the problem returns with the suspect ECM, replace the ECM.

  7. Verify that the repair eliminates the problem.

  STOP

Test Step 4. Insert a Jumper Wire at the Switch.

1. Turn the ignition key switch to the OFF position.

2. Reconnect the ECM vehicle harness connector J1/P1.

3. Fabricate a jumper wire 100 mm (4 inch) long. Crimp a Deutsch pin to each end of the wire.

4. Insert the jumper wire between the two switch terminals.

5. Turn the ignition key switch to the ON position.

6. Alternately remove the jumper wire and then insert the jumper wire at the switch terminals. At the same time, watch the status screen on the electronic service tool.

Expected Result:

The switch status changes to "ON" with the jumper wire in place. The switch status changes to "OFF" when the jumper wire is removed.

Results:

• Yes -

  Repair: Replace the switch.Verify that the repair eliminates the problem.

  STOP

• No - There is a problem in the wire harness between the switch and the ECM. Proceed to Test Step 5.

Test Step 5. Insert a Jumper Wire at the Bulkhead Connector.

1. Turn the ignition key switch to the OFF position.

2. Fabricate a jumper wire 100 mm (4 inch) long. Crimp a Deutsch pin to each end of the wire.

3. Locate the suspect switch socket in the engine side of the ECM bulkhead connector.

4. Insert the wire jumper pin between the switch socket and the sensor common connection. Install the jumper wire on the engine side of the ECM bulkhead connector.

5. Turn the ignition key switch to the ON position.

6. Alternately connect and then disconnect the jumper wire. At the same time, monitor the status screen on the electronic service tool.

Expected Result:

The switch status changes from "ON" with the jumper wire in place. The switch status changes to "OFF" when the jumper wire is removed.

Results:

• Yes - The problem is in the vehicle wiring between the bulkhead connector and the switch. Inspect the vehicle wiring and then repair the vehicle wiring. Otherwise, send the vehicle to the OEM dealer for repair. Verify that the original condition is resolved.STOP

• No - The problem is in the vehicle wiring between the bulkhead connector and the ECM. Inspect the vehicle wiring and then repair the vehicle wiring. Otherwise, send the vehicle to the OEM dealer for repair. Verify that the original condition is resolved. STOP